1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus and method. For example, an apparatus and method of a so-called tandem system which has a latent image forming unit for each of toner colors, the latent image forming unit makes a light beam from a light source scan by means of an oscillating deflection mirror surface. For another example, an apparatus and method which forms a linear latent image on a latent image carrier driven in a sub scanning direction by irradiating a latent-image forming light beam on the latent image carrier in a main scanning direction. For still another example, an apparatus and method which performs a printing operation in which a latent image is formed on a latent image carrier driven in a sub scanning direction by irradiating a latent-image forming light beam on the latent image carrier in a main scanning direction, and then, a toner image which is formed by developing the latent image is transferred onto a recording medium. The present invention also relates to a data control device suitable for use in the image forming apparatus and method above.
2. Description of the Related Art
As an image forming apparatus of this type, there has conventionally been known an image forming apparatus of a so-called tandem system wherein an image forming device including a photosensitive member, an exposure unit and a developing unit is dedicated to each of the four different colors including yellow, magenta, cyan and black, for example. In the tandem apparatus, a toner image of each color component is formed on the photosensitive member in the following manner as described in Japanese Unexamined Patent Publication No. H1-170958 of 1989, for example. That is, a light source of the exposure unit for each color component is controlled based on image data representing a toner image of the associated color component, while the light beam from the light source scans in the main scanning direction by means of a deflector (a polygon mirror, for example) of the exposure unit, thereby forming, on the photosensitive member, a latent image corresponding to the image data related to the color component. Such latent images are developed with toners of respectively corresponding colors so as to form toner images of the plural colors, and the resultant toner images of the plural colors are mutually superimposed on a transfer medium so as to form a color image.
Further, in order to achieve the size reduction and speeding up of a deflector, an apparatus has heretofore been proposed which employs an oscillating mirror as the deflector, which sinusoidally oscillates a deflection mirror surface (see, for example, Japanese Unexamined Patent Publication No. H9-230276 of 1997). In this apparatus, a frequency of a driving signal applied to the oscillating mirror matches with an intrinsic resonant frequency of the oscillating mirror, thereby bringing the oscillating mirror into resonant oscillations at relatively large amplitude. The light beam from the light source is irradiated on the oscillating mirror in resonant oscillations, thereby making the light beam scan reciprocally. Thus, the latent images are formed by the scanning light beam in both of the forward and backward scanning directions.
Furthermore, there is an image forming apparatus which is designed to print in various modes for the sake of enhancing the versatility of the apparatus and of offering sophisticated features. For instance, the apparatus described in above-mentioned Japanese Unexamined Patent Publication No. H1-170958 of 1989 is designed to print at two resolutions. In this apparatus, a polygon mirror is provided for the light beam to scan, the polygon mirror driven into rotation by a mirror driving motor. The mirror driving motor is electrically connected to a mirror driving control circuit, such that a driving signal applied to the mirror driving motor is switched between one for the lower resolution and the other for the higher resolution. In the case of printing at the lower resolution, therefore, the low-resolution driving signal is applied to the mirror driving motor so that the polygon mirror is rotated at a relatively lower speed. In the case of printing at the higher resolution, on the other hand, the high-resolution driving signal is applied to the mirror driving motor so that the polygon mirror is rotated at a relatively higher speed. By changing the rotational speed of the polygon mirror in this manner, it is possible to print in the two kinds of print modes including high-resolution printing and low-resolution printing.